2391 Revision

Introduction
The 2391 Theory examination is ‘closed book’,
in other words you cannot take any reference
books into the examination room.
However in order to work through the questions
you will be required to make reference to the
following publications:
BS 7671, On-Site Guide and Guidance Notes 3

Please remember
You will find questions that you cannot attempt
because you have not yet covered those
particular items. Do not be put off. All areas
will be covered in due course

Please remember
When carrying out questions involving
calculations you will need to use factors from
IEE publications. During the examination
ALL factors will be given in the examination
paper

Sample Questions
These questions are similar to those
that you will find in the examination.
They are Centre devised and not taken
from past City & Guilds papers

Question 1.
State TWO statutory documents that an
inspecting engineer would need knowledge
of, in order to work safely.
1. The Health and Safety at Work Act 1974
2. The Electricity @ Work Regulations 1989

1.
State three requirements relating to the isolation
of the mains supply prior to undertaking work on
a circuit. Verify supply dead using approved voltage
indicator. Apply „locking off‟ device to secure isolator
in the „off‟ position
3.
2. Apply „lock out‟ tags
.Question 4.

burns
. shock
2. fire
3. explosion
5.
State the FIVE types of injury detailed within the
Electricity at Work Regulations 1989 that may
result from the use of electrical energy
1. arcing
4.Question 5.

Question 6.
State the maximum and minimum values of voltage
covered by the Electricity at Work Regulations 1989
There are no specific values
All voltages are included
.

Question 7. Must have a good working knowledge of statutory and non-statutory
regulations appertaining to the work to be undertaken
4. Must have suitable electrical knowledge
3.
State the competence required by the person
undertaking an inspection and test of an electrical
installation
1. Must be experienced in the type of installation or system to be
worked on
2. Must be aware of the dangers that may be present during the
inspection and testing process to oneself and others that may be
using the installation
. Must understand the use of and be able to safely use test equipment
5.

State THREE requirements of the Electricity at
Work Regulations covering the use of test
equipment
1. Must be regularly maintained
Watch this one.Question 8. it always causes problems
. Must be suitable for its intended use or purpose
2. Must be used in such a manner so as not to cause danger
3.

Functional earthing conductor.
State the name and colour of the conductor
which connects the main earthing terminal
of a consumers installation. coloured
cream
.
in order for its correct operation.Question 12. to equipment.

State THREE methods which may be used
to reduce the resistance of an earth
electrode
additional earth electrodes
increasing the buried depth
soil conditioning
.Question 13.

an insulation resistance tester
must be capable of delivering a current of:
1 mA
.
In order to maintain the correct output
voltage.Question 15.

Question 16.
.
if the maximum tabulated value of
impedance Zs. for the circuit is 2 (Uo =230V)
Current required to cause operation:
I = Uo/Zs = 230/2 = 115A.
State the minimum level of operating
current required for an overcurrent device.

device must trip within 200 ms
5 x I n .0 x I n .5 x I n .
that would need to be applied to a 30mA
residual current device
0.Question 18.device must not trip
1.
State the tests.device must trip within 40 mS
. including operating times.

(including operating times).
that would need to be applied to a 100mA
residual current device
0.
.device must not trip
1.device must trip within 200 ms
5 x I n .Question 19.
State the tests.0 x I n .5 x I n . 100mA device
would not be used for personal protection.test not required.

State the three signatories required on an
installation certificate
person responsible for the design
person responsible for erection
person responsible for testing
.Question 20.

When undertaking an earth fault loop
impedance (Zs) test on an r. the device operates before a reading
can be obtained.c. protected
circuit. assumes fault
condition)
b.Question 21.d. what can be done to obtain a value of Zs
a.c. use of ‘D-LOK‟ or by calculation:
Zs = Ze + (R1+R2)
. Explain:
a.d. why the device operates
b. device operates due to test current being
passed to earth (r.

Zs = Ze + (R1+R2)
. why the device operates
b.
When undertaking an earth fault loop
impedance (Zs) test on a lighting circuit
protected by a 6A type B. what can be done to obtain a value of Zs
a. BS EN 60898 circuit
breaker.Question 22. by calculation. the device operates before a reading
can be obtained.
Explain:
a. device operates due to test current being
applied between phase and earth
b.

we do not temporarily replace the
6 amp circuit breaker with one of ten
amp rating!”
.“No.

isolate the supply prior to removing bonding
conductors
a. state
why it is necessary to:
a. Protective conductors must MUST NOT be
removed/disconnected whilst supply is live. due
to the possible risk of electric shock
. To remove parallel earth paths
b.Question 24
When verifying the external earth fault loop
impedance Zs at the origin of an installation. remove bonding conductors
b.

SELV
b.Question 25
State TWO methods of protection against both
direct and indirect contact (shock) as recognised by
BS 7671
a. limitation of discharge energy
.

TN-C-S
. TT
b. TN-S
c. the value of prospective earth fault
current and prospective short circuit current were of
equal value. The type of earthing arrangement
involved would be:
a.Question 29
When measured at the origin of an electrical
installation.

details of the client
b. extent and limitation of the inspection and test
d. schedule of test results
f. recommendations
.Question 30
State the information contained within a periodic
inspection and test report :
a. characteristics of the supply
c. schedule of items inspected
e.

93
Therefore approximate value of R1+R2
= 1.99
c.c.Question 31
The end to end resistance of each of the three rings
of a 30A ring circuit were measured and gave the
following results:
phase/phase ring . ring
= 0.482
.p.96 + 0.p./c.93/4 = 0.0.0.97
Determine an approximate value of R1+R2 for this
circuit.96
neutral/neutral ring .
By adding the phase and c.c. ring
.97= 1.c.0.p.

(T & c.p.
Calculate the approximate length of the circuit.c.
From Table 1A GN3 (page 107) R1+R2/metre = 19. copper
conductor cable).c.c.v.51 = 25 metres
.
Phase and c.2. the value of R1+R2 was found to be
0.488.p. (ambient temperature 20°C). general purpose p. for A3 radial .5mm2.5/1.Question 32
When measured at the furthest point on an A3 radial
circuit.51m
Convert 0.488 to m = 488
Therefore length of circuit in = 488/19.

.Bet you found the last
one easy! HaHa.

R.Question 33
State FOUR items of electrical equipment that
would require functional testing during an
inspection and test.D.‟s
switches of socket outlet
isolators
circuit breakers
.C.

T
k
.Question 34
State the equation that may be applied in
order to reduce the cross-sectional area of
circuit protective conductors
The adiabatic equation
s=
2
I .

Remember Peter Periodic
Continuity
Polarity
Earth fault loop
Insulation resistance
Functional
Can
Peter
Ever
Inspect
Forever
.Question 35
State in the correct sequence the first five tests to
be applied during a periodic inspection and test of
an electrical installation.

d protecting a circuit in a
domestic electrical installation.
Remember! Very shortly this value is to be reduced to
a maximum of 100
.c.Question 36
Determine the maximum permitted earth electrode
resistance for a 100mA r.1 = 500
In practice it is recommended that an earth electrode
resistance in excess of 200 is unacceptable.
Zs = 50V/0.

which
other TWO tests are automatically carried out?
Determination of R1+R2.Question 37
When undertaking a ring final circuit test. and
Polarity
.

10.5M
c.5M
b. 1.
.Question 38
Which ONE of the following values of insulation
resistance may indicate a latent defect?
a. 2.0M may be indicative of
a latent defect.0M
d. 25M
Remember! A value below 2.

Question 39
When undertaking a site applied insulation test.c.
. for a period of 60 seconds
Remember! During the 60 seconds test period
flashover should not occur. 5000V a.c. for a period of 60 seconds
c.c. the
following applied voltage and test duration should be
adhered to:
a. 5000V d.c. 3750V d. 3750V a. for a period of 60 seconds
d. for a period of 60 seconds
b.

b.
d.0 x I
5 I
Functional test
Five times test for supplementary protection against
direct contact.5 x I
1.Question 40
Which ONE of the following tests would NOT be
applied to a 500mA residual current device?
a. 500mA for thermal protection
.
c.
0.

State where
the test should be conducted and the type of test
equipment to be used.
To ensure that the PES polarity is correct.Question 42
Explain why it would be necessary to undertake a live
polarity test on an electrical installation.
Test to be carried out at the main distribution board
Use of approved voltage indicator to GS 38
.

Question 43
A continuity test was undertaken on four equipotential
bonding conductors. The results of these tests are
listed below. Which of the four readings is not
acceptable?

a. 0.01
b. 45m
c. 0.04
d. 55m
Resistance of any bonding conductor not to be greater
than 0.05, 50m

Question 44
State THREE requirements of BS 7671 with regard to
the inspection of installed electrical equipment:

• equipment to British or harmonised standard
• correctly selected and erected
• not visibly damaged or defective so as to impair
safety

Question 45 (answer on next slide)
Four final circuits are fed from the distribution board as
shown. When measured individually, the value of
insulation resistance for each circuit is as follows:
circuit a 50M
circuit b 100M
circuit c 20M
circuit d 10M

Determine the collective
value of insulation resistance
if measured from the incoming
tails at the distribution board

d.c.Question 46
State the unit of measurement for each ONE of the
following tests:
• impedance
•insulation resistance
•prospective fault current
•r. test
•continuity
Ohms ()
meggohms
kilo-amps (kA)
milliseconds
Ohms ()
.

0. 0.6
. Calculate the following values
of resistance for this cable:
a. the resistance of 500 metres of one core
c.2.6
c.Question 47
The total resistance of one core of a 1000 metre drum
of 2 -core cable is 1. the total resistance of both cores for 1000 metres
b.4
b. 2. the resistance of one core of 1000 metre length if the
cross-sectional are was doubled
a.

Do Not Remove
Safety Earthing Connection -Do Not Remove
. The wording
on the label should state:
•
•
•
•
Safety Earth Connection .Question 51
A permanent label to BS 951 should be fixed in
a visible position at points of connection to every
earth electrode or bonding position.Do Not Remove
Safety Electrical Connection .Do Not Remove
Safety Earth Point .

Question 52
State the information that should be contained
on a label adjacent to every fuse or circuit
breaker
• the size and type of fuse or circuit breaker
• identification of the protected circuit
.

at or near the origin of the installation.Question 53
A notice should be fixed in a prominent position. Sate the
two pieces of information that should appear on
the notice.
The notice relates to periodic inspection and should
state:
• the date of the last inspection
• recommended date of the next inspection
.

Question 54
Identify Four locations within an electrical
installation where impedance tests would need
to be carried out
•
•
•
•
the origin of the installation (Ze)
at each distribution board
at each socket outlet
at the furthest extremity of every radial circuit
.

the supply authority has inspected the installation
. both live and dead tests have been completed
c. defects have been remedied
b. the inspecting engineer has identified all defects
d.Question 55
An Installation Certificate should only be issued
when:
a.

b.
c.
10 A
15 A
25 A
50 A
.
d. the maximum current
need not exceed :
a.Question 56
When undertaking a high current continuity test
on a ferrous enclosure.

Question 57
State the title of:
a. the person responsible for inspection and test
a. competent person
. duty holder
b. the person who has an installation or system
under their control
b.

The installation is approximately twenty
five years old and does not have a current test
certificate. Sate the type(s) of certification required for
this installation.Question 61
An electrical contractor is requested to install a motor
circuit and replace several defective fluorescent
lighting fittings.
• installation certificate for new motor circuit
• minor works certificate for new lighting fittings
• periodic inspection certificate for existing
installation
.

Table 1A (GN3) R1 + R2 /metre = 19.Question 62
An A1 ring circuit has a length 50 metres and wired in
general purpose p. the value of (R1+R2) of the ring circuit when
measured at 20°C
a. for A1 ring circuit R1 + R2 will be 2. Determine:
a.c.51m/m
.5mm2
respectively.5/1. the resistance of each ring when measured at 20°C
b.v. insulated cables having copper
conductors.

warning notices/labels
distribution charts.
2. diagrams etc etc
presence of earthing and bonding conductors
selection of live conductors in relation to current
carrying capacity and voltage drop
rating/setting of overcurrent devices
identification of conductors
methods of protection against direct/indirect shock
Location of devices for isolation and switching
.
4.
6.
3.
8.
5.
7.Question 64
State FIVE specific areas of inspection when
undertaking an inspection and test on a light industrial
workshop:
1.

5.
4.Question 65
State the first FIVE tests to be undertaken on an A1
ring circuit during an initial verification:
1.
continuity of c.
2.c.’s including bonding conductors
continuity of ring final circuit conductors
insulation resistance
polarity
earth loop impedance
.
3.p.

a circuit is removed
a. removing circuits will increase the overall value of
insulation resistance
. adding circuits will decrease the overall value of
insulation resistance
b.Question 66
State the overall effect on the insulation resistance of
an installation when:
a. a circuit is added
b.

5 
Determine:
a.2 
• phase . the prospective earth fault current
b.earth 0. estimated value of prospective fault current
between two phases
.Question 67
An instrument used to measure the impedance at the
incoming terminals of a 400/230V three phase TN-S
system indicates the following results:
• phase .neutral 0. prospective short circuit current
c.

Question 68
State FIVE reasons why an installation will need to
undergo a periodic inspection and test:
•
•
•
•
•
current certificate time expired
as a result of damage
change of ownership
change of use
mortgage/building society requirements
.

Question 69
State FIVE bodies or organisations that may be
involved with the preparation of a specification for an
electrical installation:
•
•
•
•
•
•
designer
installer
PES
architect
fire prevention officer
Health & Safety Executive
.

the qualifying manager
d.Question 72
A periodic inspection and test report should be signed
by:
a. the person ordering the work
b. a person holding recognised qualifications in the
inspection and testing of electrical installations
. a competent person
c.

a person holding recognised qualifications in the
inspection and testing of electrical installations
. the qualifying manager
d. a competent person
c.Question 73
A periodic inspection and test report should be signed
by:
a. the person ordering the work
b.

a single circuit is added to an existing installation
b. the inspecting engineer is not authorised to issue a
periodic inspection and test report
d.Question 74
A minor works certificate would be issued when:
a. alterations or additions are made to an existing
installation
c. the person erecting the installation is also
responsible for the design and testing
.

Question 75
A Short form of Electrical Installation Certificate may be
issued when:
a. undertaking electrical installations within domestic
properties
b. one person is responsible for the design. the current demand of the installation does not
exceed 100A
. Undertaking minor works
c. construction
and inspection and testing of an installation
d.

Question 76
State the information that should be made available to
the person carrying out an inspection and test:
• Maximum demand after the application of diversity
• number and type of live conductors of the source of
energy and of the circuits used in the installation
• the type of earthing arrangement
• type and composition of circuits
• description and location of devices performing the
functions of protection or isolation
• methods selected to prevent danger from shock in
the event of an earth fault
• any circuit or equipment vulnerable to testing
.

c. Class II installation
b. EEBADOS
d. provided its rated tripping current does not
exceed 30mA
.Question 77
Which ONE of the following will provide protection
against both direct and indirect contact?
a.d. SELV
c. an r.

barriers and enclosures
d. Earth-free local equipotential bonding
. non-conducting location
b. SELV
c.Question 78
Which ONE of the following will NOT provide protection
against indirect contact?
a.

quarterly
d. monthly
c. weekly
b. annually
.Question 80
Where an installation is protected by a residual current
device it should be manually tested by use of the
integral test button:
a.

Question 81
Where diagrams. charts or tables are not available
during a periodic inspection:
a. a degree of exploratory work may be necessary
d. all work should cease and the client informed
accordingly
b. it should be recorded in the extent and limitations
. testing should be carried out in place of the visual
inspection
c.

Question 89
Which of the following actions would be INCORRECT
when undertaking an insulation resistance test on a
230V discharge lighting circuit. testing between neutral conductor and earth with
the local switch in the on position
d. disconnecting voltage sensitive devices
.:
a. testing between live conductors with the local
switch in the on position
b. testing between phase conductor and earth with the
local switch in the on position
c.

100mA
d.’ some instruments
reduce the possibility of r. 30mA
c.Question 90
As an alternative to the ‘D-Lok.d. tripping during impedance
testing by limiting the test current to:
a. 150mA
. 15mA
b.c.